1. Field of the Invention
The present invention relates to a method for preparing nicotianamine or a nicotianamine-containing product which has angiotensin converting enzyme (ACE) inhibitory activity from an aqueous extract of soybeans and to a health food containing the nicotianamine-containing product as a functional ingredient.
2. Description of the Related Art
Nicotianamine has blood pressure lowering action based on ACE inhibition. Nicotianamine is widely found in the vegetable world, such as tobaccos, rice plants, Chinese matrimony vines, and beeches, and are obtainable from the leaves of these plants (JP-A-63-87990). It is known that nicotianamine is also found in kidney beans and soybeans and that an extract of the beans with water or hot water is treated with a synthetic resin to obtain purified nicotianamine (JP-A-5-246865).
However, the method of obtaining nicotianamine through extraction of plant leaves meets difficulty in stably securing a large quantity of the plant. Since production of kidney beans is very low, it tends to be difficult to procure a stable supply as a raw material of nicotianamine.
On the other hand, soybeans are stably supplied. However, where nicotianamine is prepared from an aqueous extract of soybeans, such as a boiling waste liquid or a soaking waste liquid in the soybean processing industry, by adsorption and desorption by a synthetic resin, the yield is low, resulting in a high cost.